This invention relates to a new aqueous slurry process which will effectively remove heavy metals from solids. The process involves mixing solid ion exchange material with contaminated solids in an aqueous liquid. Due to the high ionic activity of the ion exchange material, the contaminant will have a strong affinity for that material, and will thus move from the contaminated solid to the solid ion exchange material, with minimal contaminant concentration in solution.
The contamination of soils, sludges, ashes, and other solids by heavy metals or radioactive species is a significant environmental problem. Typically, large volumes are involved, and disposal costs for these solids are becoming extremely expensive. There is thus tremendous incentive to reduce the volume of waste requiring disposal. It has been found that a certain fraction of the contaminants present in solids is readily mobilized. Unfortunately, in many cases the amount of contaminant removed is not sufficient to reach the low residual environmental levels required by such groups as the Environmental Protection Agency, Nuclear Regulatory Commission, and various state regulatory agencies. The remaining fraction of contaminants is typically adsorbed or otherwise bound onto the solids, making removal difficult.
In many instances, .the contaminant on the material, is extracted or dissolved in acid or base to produce a solution containing the metal. The contaminated solution is then separated from the material and further treated. The contaminant can then be removed from the solution. In the process of U.S. Pat. No. 4,808,318 (Komarneni et al.), hydrated sodium phlogopite mica, selective as to Cs, is used to remove Cs from a chloride solution. There, powdered phlogopite mica ion exchange material is mixed with CsCl solution for 4 days. The Cs is absorbed by the mica and fixed in the mica structure, not subject to displacement. The loaded ion exchange material is hen removed by a centrifuge. Passing the solution through a packed bed or column of the ion exchange mica is also taught.
In another attempt to remove contaminants, U.S. Pat. No. 4,783,263 (Trost et al.) teaches a process involving collecting contaminated soils, sludges, sediments, clays or the like, converting it into a slurry, and then adding surfactants, such as alphaolefin sulfonate, to desorb the contaminating metal or the like and place it in the liquid phase of the slurry, which liquid is concentrated as to the contaminant in a series of flotation cells and then disposed of. Neither of these processes is completely effective.
What is needed is an inexpensive process to dramatically lower contaminants such as Cu, Pb, Ce, Cd, U and the like, in an aqueous process which starts with contaminated soil. It is the main object of this invention to provide such a process.